diff --git a/emcc.py b/emcc.py
index f9e2929f0557c..e4a670ac0a33f 100755
--- a/emcc.py
+++ b/emcc.py
@@ -2363,20 +2363,21 @@ def do_binaryen(final, target, asm_target, options, memfile, wasm_binary_target,
   if options.opt_level >= 2:
     # minify the JS
     optimizer.do_minify() # calculate how to minify
-    if optimizer.cleanup_shell or optimizer.minify_whitespace or options.use_closure_compiler:
-      misc_temp_files.note(final)
+    if optimizer.cleanup_shell or options.use_closure_compiler:
       if DEBUG: save_intermediate('preclean', 'js')
+      # in -Os and -Oz, run AJSDCE (aggressive JS DCE, performs multiple iterations)
+      passes = ['noPrintMetadata', 'JSDCE' if options.shrink_level == 0 else 'AJSDCE', 'last']
+      if optimizer.minify_whitespace:
+        passes.append('minifyWhitespace')
+      misc_temp_files.note(final)
+      logging.debug('running cleanup on shell code: ' + ' '.join(passes))
+      final = shared.Building.js_optimizer_no_asmjs(final, passes)
+      if DEBUG: save_intermediate('postclean', 'js')
       if options.use_closure_compiler:
         logging.debug('running closure on shell code')
+        misc_temp_files.note(final)
         final = shared.Building.closure_compiler(final, pretty=not optimizer.minify_whitespace)
-      else:
-        assert optimizer.cleanup_shell
-        logging.debug('running cleanup on shell code')
-        passes = ['noPrintMetadata', 'JSDCE', 'last']
-        if optimizer.minify_whitespace:
-          passes.append('minifyWhitespace')
-        final = shared.Building.js_optimizer_no_asmjs(final, passes)
-      if DEBUG: save_intermediate('postclean', 'js')
+        if DEBUG: save_intermediate('postclosure', 'js')
   # replace placeholder strings with correct subresource locations
   if shared.Settings.SINGLE_FILE:
     f = open(final, 'r')
diff --git a/tests/optimizer/AJSDCE-output.js b/tests/optimizer/AJSDCE-output.js
new file mode 100644
index 0000000000000..b4804b9429bf2
--- /dev/null
+++ b/tests/optimizer/AJSDCE-output.js
@@ -0,0 +1,27 @@
+
+var z = fleefl();
+var zz = fleefl();
+function g(a) {
+ return a + 1;
+}
+Module["g"] = g;
+function h(a) {
+ return a + 1;
+}
+print(h(123));
+((function() {
+ var z = fleefl();
+ var zz = fleefl();
+ function g(a) {
+  return a + 1;
+ }
+ Module["g"] = g;
+ function hh(a) {
+  return a + 1;
+ }
+ print(hh(123));
+}))();
+function glue() {
+}
+glue();
+
diff --git a/tests/optimizer/AJSDCE.js b/tests/optimizer/AJSDCE.js
new file mode 100644
index 0000000000000..ca1c133929fee
--- /dev/null
+++ b/tests/optimizer/AJSDCE.js
@@ -0,0 +1,61 @@
+
+// all unused
+var x;
+var y = 1;
+var z = fleefl();
+var xx, yy = 1, zz = fleefl(); // but zz must remain due to the side effects in the value
+function f(x, y, z) {
+  // shadow the x,y,z
+  x = y;
+  y = z;
+}
+
+// exported
+function g(a) {
+  return a+1;
+}
+Module['g'] = g;
+
+// used
+function h(a) {
+  var t; // unused
+  return a+1;
+}
+print(h(123));
+
+// inner workings
+(function() {
+  var x;
+  var y = 1;
+  var z = fleefl();
+  var xx, yy = 1, zz = fleefl();
+  function f(x, y, z) {
+    // shadow the x,y,z
+    x = y;
+    y = z;
+  }
+
+  // exported
+  function g(a) {
+    return a+1;
+  }
+  Module['g'] = g;
+
+  // used
+  function hh(a) {
+    var t; // unused
+    return a+1;
+  }
+  print(hh(123));
+})();
+
+function glue() {
+  function lookup() { // 2 passes needed for this one
+    throw 1;
+  }
+  function removable() { // first remove this
+    lookup();
+  }
+}
+glue();
+
diff --git a/tests/optimizer/JSDCE-output.js b/tests/optimizer/JSDCE-output.js
index efa7528d0975a..50194093bf33b 100644
--- a/tests/optimizer/JSDCE-output.js
+++ b/tests/optimizer/JSDCE-output.js
@@ -21,4 +21,10 @@ print(h(123));
  }
  print(hh(123));
 }))();
+function glue() {
+ function lookup() {
+  throw 1;
+ }
+}
+glue();
 
diff --git a/tests/optimizer/JSDCE.js b/tests/optimizer/JSDCE.js
index d496992bfe052..ca1c133929fee 100644
--- a/tests/optimizer/JSDCE.js
+++ b/tests/optimizer/JSDCE.js
@@ -49,3 +49,13 @@ print(h(123));
   print(hh(123));
 })();
 
+function glue() {
+  function lookup() { // 2 passes needed for this one
+    throw 1;
+  }
+  function removable() { // first remove this
+    lookup();
+  }
+}
+glue();
+
diff --git a/tests/test_core.py b/tests/test_core.py
index 9ace433518354..c8486349ab354 100644
--- a/tests/test_core.py
+++ b/tests/test_core.py
@@ -55,6 +55,13 @@ def is_split_memory(self):
   def is_wasm(self):
     return 'BINARYEN' in str(self.emcc_args) or self.is_wasm_backend()
 
+  # Use closure in some tests for some additional coverage
+  def maybe_closure(self):
+    if '-O2' in self.emcc_args or '-Os' in self.emcc_args:
+      self.emcc_args += ['--closure', '1']
+      return True
+    return False
+
   def do_run_in_out_file_test(self, *path, **kwargs):
       test_path = path_from_root(*path)
 
@@ -882,8 +889,7 @@ def test_exceptions(self):
       Settings.EXCEPTION_DEBUG = 1
 
       Settings.DISABLE_EXCEPTION_CATCHING = 0
-      if '-O2' in self.emcc_args:
-        self.emcc_args += ['--closure', '1'] # Use closure here for some additional coverage
+      self.maybe_closure()
 
       src = '''
         #include <stdio.h>
@@ -4089,8 +4095,7 @@ def test_langinfo(self):
 
   def test_files(self):
     self.banned_js_engines = [SPIDERMONKEY_ENGINE] # closure can generate variables called 'gc', which pick up js shell stuff
-    if '-O2' in self.emcc_args:
-      self.emcc_args += ['--closure', '1'] # Use closure here, to test we don't break FS stuff
+    if self.maybe_closure(): # Use closure here, to test we don't break FS stuff
       self.emcc_args = [x for x in self.emcc_args if x != '-g'] # ensure we test --closure 1 --memory-init-file 1 (-g would disable closure)
     elif '-O3' in self.emcc_args and not self.is_wasm():
       print('closure 2')
@@ -5095,8 +5100,7 @@ def test_sse1(self):
     orig_args = self.emcc_args
     for mode in [[], ['-s', 'SIMD=1']]:
       self.emcc_args = orig_args + mode + ['-msse']
-      if '-O2' in self.emcc_args:
-        self.emcc_args += ['--closure', '1'] # Use closure here for some additional coverage
+      self.maybe_closure()
 
       self.do_run(open(path_from_root('tests', 'test_sse1.cpp'), 'r').read(), 'Success!')
 
@@ -5118,8 +5122,7 @@ def test_sse1_full(self):
     orig_args = self.emcc_args
     for mode in [[], ['-s', 'SIMD=1']]:
       self.emcc_args = orig_args + mode + ['-I' + path_from_root('tests'), '-msse']
-      if '-O2' in self.emcc_args:
-        self.emcc_args += ['--closure', '1'] # Use closure here for some additional coverage
+      self.maybe_closure()
 
       self.do_run(open(path_from_root('tests', 'test_sse1_full.cpp'), 'r').read(), self.ignore_nans(native_result), output_nicerizer=self.ignore_nans)
 
@@ -5141,8 +5144,7 @@ def test_sse2_full(self):
     orig_args = self.emcc_args
     for mode in [[], ['-s', 'SIMD=1']]:
       self.emcc_args = orig_args + mode + ['-I' + path_from_root('tests'), '-msse2'] + args
-      if '-O2' in self.emcc_args:
-        self.emcc_args += ['--closure', '1'] # Use closure here for some additional coverage
+      self.maybe_closure()
 
       self.do_run(open(path_from_root('tests', 'test_sse2_full.cpp'), 'r').read(), self.ignore_nans(native_result), output_nicerizer=self.ignore_nans)
 
@@ -5451,8 +5453,7 @@ def test_sqlite(self):
                  force_c=True)
 
   def test_zlib(self):
-    if '-O2' in self.emcc_args and 'ASM_JS=0' not in self.emcc_args: # without asm, closure minifies Math.imul badly
-      self.emcc_args += ['--closure', '1'] # Use closure here for some additional coverage
+    self.maybe_closure()
 
     assert 'asm2g' in test_modes
     if self.run_name == 'asm2g':
diff --git a/tests/test_other.py b/tests/test_other.py
index e4135f11c82b1..0f7fc24d82cc9 100644
--- a/tests/test_other.py
+++ b/tests/test_other.py
@@ -1973,6 +1973,8 @@ def test_js_optimizer(self):
        ['JSDCE']),
       (path_from_root('tests', 'optimizer', 'JSDCE-hasOwnProperty.js'), open(path_from_root('tests', 'optimizer', 'JSDCE-hasOwnProperty-output.js')).read(),
        ['JSDCE']),
+      (path_from_root('tests', 'optimizer', 'AJSDCE.js'), open(path_from_root('tests', 'optimizer', 'AJSDCE-output.js')).read(),
+       ['AJSDCE']),
     ]:
       print(input, passes)
 
diff --git a/tools/js-optimizer.js b/tools/js-optimizer.js
index 8f12ea89e36f9..5454c4d0e9fcd 100644
--- a/tools/js-optimizer.js
+++ b/tools/js-optimizer.js
@@ -7807,112 +7807,127 @@ function eliminateDeadGlobals(ast) {
 // Removes obviously-unused code. Similar to closure compiler in its rules -
 // export e.g. by Module['..'] = theThing; , or use it somewhere, otherwise
 // it goes away.
-function JSDCE(ast) {
-  var scopes = [{}]; // begin with empty toplevel scope
-  function DUMP() {
-    printErr('vvvvvvvvvvvvvv');
-    for (var i = 0; i < scopes.length; i++) {
-      printErr(i + ' : ' + JSON.stringify(scopes[i]));
-    }
-    printErr('^^^^^^^^^^^^^^');
-  }
-  function ensureData(scope, name) {
-    if (Object.prototype.hasOwnProperty.call(scope, name)) return scope[name];
-    scope[name] = {
-      def: 0,
-      use: 0,
-      param: 0 // true for function params, which cannot be eliminated
-    };
-    return scope[name];
-  }
-  function cleanUp(ast, names) {
+function JSDCE(ast, multipleIterations) {
+  function iteration() {
+    var removed = false;
+    var scopes = [{}]; // begin with empty toplevel scope
+    function DUMP() {
+      printErr('vvvvvvvvvvvvvv');
+      for (var i = 0; i < scopes.length; i++) {
+        printErr(i + ' : ' + JSON.stringify(scopes[i]));
+      }
+      printErr('^^^^^^^^^^^^^^');
+    }
+    function ensureData(scope, name) {
+      if (Object.prototype.hasOwnProperty.call(scope, name)) return scope[name];
+      scope[name] = {
+        def: 0,
+        use: 0,
+        param: 0 // true for function params, which cannot be eliminated
+      };
+      return scope[name];
+    }
+    function cleanUp(ast, names) {
+      traverse(ast, function(node, type) {
+        if (type === 'defun' && Object.prototype.hasOwnProperty.call(names, node[1])) {
+          removed = true;
+          return emptyNode();
+        }
+        if (type === 'defun' || type === 'function') return null; // do not enter other scopes
+        if (type === 'var') {
+          node[1] = node[1].filter(function(varItem, j) {
+            var curr = varItem[0];
+            var value = varItem[1];
+            var keep = !(curr in names) || (value && hasSideEffects(value));
+            if (!keep) removed = true;
+            return keep;
+          });
+          if (node[1].length === 0) return emptyNode();
+        }
+      });
+      return ast;
+    }
+    var isVarNameOrObjectKeys = [];
+    // isVarNameOrObjectKeys is a stack which saves the state the node is defining a variable or in an object literal.
+    // the second argument `type` passed into the callback function called by traverse() could be a variable name or object key name.
+    // You cannot distinguish the `type` is a real type or not without isVarNameOrObjectKeys.
+    // ex.) var name = true;          // `type` can be 'name'
+    //      var obj = { defun: true } // `type` can be 'defun'
     traverse(ast, function(node, type) {
-      if (type === 'defun' && Object.prototype.hasOwnProperty.call(names, node[1])) return emptyNode();
-      if (type === 'defun' || type === 'function') return null; // do not enter other scopes
+      if (isVarNameOrObjectKeys[isVarNameOrObjectKeys.length - 1]) { // check parent node defines a variable or is an object literal
+        // `type` is a variable name or an object key name
+        isVarNameOrObjectKeys.push(false); // doesn't define a variable nor be an object literal
+        return;
+      }
       if (type === 'var') {
-        node[1] = node[1].filter(function(varItem, j) {
-          var curr = varItem[0];
-          var value = varItem[1];
-          return !(curr in names) || (value && hasSideEffects(value));
+        node[1].forEach(function(varItem, j) {
+          var name = varItem[0];
+          ensureData(scopes[scopes.length-1], name).def = 1;
         });
-        if (node[1].length === 0) return emptyNode();
+        isVarNameOrObjectKeys.push(true); // this `node` defines a varible
+        return;
+      }
+      if (type === 'object') {
+        isVarNameOrObjectKeys.push(true); // this `node` is an object literal
+        return;
       }
-    });
-    return ast;
-  }
-  var isVarNameOrObjectKeys = [];
-  // isVarNameOrObjectKeys is a stack which saves the state the node is defining a variable or in an object literal.
-  // the second argument `type` passed into the callback function called by traverse() could be a variable name or object key name.
-  // You cannot distinguish the `type` is a real type or not without isVarNameOrObjectKeys.
-  // ex.) var name = true;          // `type` can be 'name'
-  //      var obj = { defun: true } // `type` can be 'defun'
-  traverse(ast, function(node, type) {
-    if (isVarNameOrObjectKeys[isVarNameOrObjectKeys.length - 1]) { // check parent node defines a variable or is an object literal
-      // `type` is a variable name or an object key name
       isVarNameOrObjectKeys.push(false); // doesn't define a variable nor be an object literal
-      return;
-    }
-    if (type === 'var') {
-      node[1].forEach(function(varItem, j) {
-        var name = varItem[0];
-        ensureData(scopes[scopes.length-1], name).def = 1;
-      });
-      isVarNameOrObjectKeys.push(true); // this `node` defines a varible
-      return;
-    }
-    if (type === 'object') {
-      isVarNameOrObjectKeys.push(true); // this `node` is an object literal
-      return;
-    }
-    isVarNameOrObjectKeys.push(false); // doesn't define a variable nor be an object literal
-    if (type === 'defun' || type === 'function') {
-      if (node[1]) ensureData(scopes[scopes.length-1], node[1]).def = 1;
-      var scope = {};
-      node[2].forEach(function(param) {
-        ensureData(scope, param).def = 1;
-        scope[param].param = 1;
-      });
-      scopes.push(scope);
-      return;
-    }
-    if (type === 'name') {
-      ensureData(scopes[scopes.length-1], node[1]).use = 1;
-    }
-  }, function(node, type) {
-    isVarNameOrObjectKeys.pop();
-    if (isVarNameOrObjectKeys[isVarNameOrObjectKeys.length - 1]) return; // `type` is a variable name or an object key name
-    if (type === 'defun' || type === 'function') {
-      var scope = scopes.pop();
-      var names = set();
-      for (name in scope) {
-        var data = scope[name];
-        if (data.use && !data.def) {
-          // this is used from a higher scope, propagate the use down
-          ensureData(scopes[scopes.length-1], name).use = 1;
-          continue;
-        }
-        if (data.def && !data.use && !data.param) {
-          // this is eliminateable!
-          names[name] = 0;
+      if (type === 'defun' || type === 'function') {
+        if (node[1]) ensureData(scopes[scopes.length-1], node[1]).def = 1;
+        var scope = {};
+        node[2].forEach(function(param) {
+          ensureData(scope, param).def = 1;
+          scope[param].param = 1;
+        });
+        scopes.push(scope);
+        return;
+      }
+      if (type === 'name') {
+        ensureData(scopes[scopes.length-1], node[1]).use = 1;
+      }
+    }, function(node, type) {
+      isVarNameOrObjectKeys.pop();
+      if (isVarNameOrObjectKeys[isVarNameOrObjectKeys.length - 1]) return; // `type` is a variable name or an object key name
+      if (type === 'defun' || type === 'function') {
+        var scope = scopes.pop();
+        var names = set();
+        for (name in scope) {
+          var data = scope[name];
+          if (data.use && !data.def) {
+            // this is used from a higher scope, propagate the use down
+            ensureData(scopes[scopes.length-1], name).use = 1;
+            continue;
+          }
+          if (data.def && !data.use && !data.param) {
+            // this is eliminateable!
+            names[name] = 0;
+          }
         }
+        cleanUp(node[3], names);
+      }
+    });
+    // toplevel
+    var scope = scopes.pop();
+    assert(scopes.length === 0);
+
+    var names = set();
+    for (var name in scope) {
+      var data = scope[name];
+      if (data.def && !data.use) {
+        assert(!data.param); // can't be
+        // this is eliminateable!
+        names[name] = 0;
       }
-      cleanUp(node[3], names);
-    }
-  });
-  // toplevel
-  var scope = scopes.pop();
-  assert(scopes.length === 0);
-
-  var names = set();
-  for (var name in scope) {
-    var data = scope[name];
-    if (data.def && !data.use) {
-      assert(!data.param); // can't be
-      // this is eliminateable!
-      names[name] = 0;
     }
+    cleanUp(ast, names);
+    return removed;
   }
-  cleanUp(ast, names);
+  while (iteration() && multipleIterations) { }
+}
+
+// Aggressive JSDCE - multiple iterations
+function AJSDCE(ast) {
+  JSDCE(ast, /* multipleIterations= */ true);
 }
 
 function removeFuncs(ast) {
@@ -7961,6 +7976,7 @@ var passes = {
   dumpCallGraph: dumpCallGraph,
   asmLastOpts: asmLastOpts,
   JSDCE: JSDCE,
+  AJSDCE: AJSDCE,
   removeFuncs: removeFuncs,
   noop: function() {},